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For Better View Of This Web Page, Please Use Any Latest Web Browser, Because Some Elements Are Not Work In The Old Web Browser (Might Not Be Displayed Properly Or Are Not Appearing properly!). Plz Note: Some Topics That You Might Want To Pursue On Your Own That We Did Not Cover In This Article Are Listed Here. This Page Discusses “LAYER 2, LAYER 3AND LAYER 4 SWITCH COMPARISON”, And Also We Request To The Students, Please Go Through All The Articles That Are We Posted In This Web Site And Also Identify All The CISCO IOS Commands In The Lab Practice Before Going To Access This Page. Thank You!OSI LAYER 2 (DATA LINK LAYER), AND OSI LAYER 3 (NETWORK LAYER), AND ALSO OSI LAYER 4 (TRANSPORT LAYER):
A Layer 2 Switch, Makes Forwarding Decisions Based On L2 (MAC) Addresses. We Would Normally Just Call This Device A Switch. Layer 2 Switching Is Hardware Based, Which Means It Uses The Media Access Control (MAC) Address From The Host's Network Interface Cards (NICs) To Filter The Network. Layer 2 Switches Use Application-Specific Integrated Circuits. (ASICs) To Build And Maintain Filter Tables.
◙ MEDIA ACCESS CONTROL (MAC): The Media Access Control (MAC) Layer Defines Specifications For Controlling Access To The Media. The MAC Sublayer Is Responsible For:
• Adding Frame Start And Stop Information To The Packet
• Adding Cyclical Redundancy Check (CRC) For Error Checking
• Converting Frames Into Bits To Be Sent Across The Network
• Identifying Network Devices And Network Topologies In Preparation For Media Transmission
• Defining An Address (Such As The MAC Address) For Each Physical Device On The Network
• Controlling Access To The Transmission Medium
◙ LOGICAL LINK CONTROL (LLC):
The Logical Link Control (LLC) Layer Provides An Interface Between The MAC Layer And Upper-Layer Protocols. LLC Protocols Are Defined By The IEEE 802.2 Committee. The LLC Sublayer Is Responsible For:
• Maintaining Orderly Delivery Of Frames Through Sequencing
• Controlling The Flow Or Rate Of Transmissions Using The Following:
• Acknowledgements
• Buffering
• Windowing
• Ensuring Error-Free Reception Of Messages By Retransmitting
• Converting Data Into An Acceptable Form For The Upper Layers
• Removing Framing Information From The Packet And Forwarding The Message To The Network Layer
• Provide A Way For Upper Layers Of The OSI Model To Use Any MAC Layer Protocol
• Defining Service Access Points (Saps) By Tracking And Managing Different Protocols.
◙ - ➤ OSI LAYER 3- NETWORK LAYER:
The Network Layer Is Concerned With Packet Switching. It Establishes Virtual Circuits (Paths Between Terminals) For Data Communications. As The Sending End, The Network Layer Repackages Messages From The Transport Layer Above It Into Data Packets, So The Lower Layers Can Transmit Them.
The Network Layer Describes How Data Is Routed Across Networks And On To The Destination. Network Layer Functions Include:
• Maintaining Addresses Of Neighboring Routers.
• Maintaining A List Of Known Networks.
• Determining The Next Network Point To Which Data Should Be Sent. Routers
• Use A Routing Protocol To Take Into Account Various Factors Such As The Number Of Hops In The Path, Link Speed, And Link Reliability To Select The Optimal Path For Data.
• Packets Forwarded From The Transport To The Network Layer Become Datagrams And Network-Specific (Routing) Information Is Added. Network Layer Protocols Then Ensure That The Data Arrives At The Intended Destinations.
A Layer 3 Switch, Makes Forwarding Decisions Based On L3 (IP) Addresses. ◙ - ➤ LAYER 4 - TRANSPORT LAYER:
The Transport Layer Of The OSI Model Has Many Functions, Including Several Order F Error Recognitions And Recoveries. As The Highest Order, The Transport Layer Can Detect Errors, Identify Packets That Have Been Sent In The Incorrect Order, And Then Rearrange Them. The Transport Layer Also Regulates The Information Flow By Controlling The Messages Movements.
• Port (Or Socket) Numbers Are Used To Identify Distinct Applications Running On The Same System. This Allows Each Host To Provide Multiple Services.
• The Transport Layer Receives Large Packets Of Information From Higher Layers And Breaks Them Into Smaller Packets Called Segments. Segmentation Is Necessary To Enable The Data To Meet Network Size And Format Restrictions.
• The Receiving Transport Layer Uses Packet Sequence Numbers To Reassemble Segments Into The Original Message.
• Connection-Oriented Protocols Perform Error Detection And Correction And Identify Lost Packets For Retransmission. A Connection-Oriented Protocol Is A Good Choice Where:
• Reliable, Error-Free Communications Are More Important Than Speed
• Larger Chunks Of Data Are Being Sent
• Connectionless Services Assume An Existing Link Between Devices And Allow Transmission Without Extensive Session Establishment. Connectionless Communications Use No Error Checking, Session Establishment, Or Acknowledgements. Connectionless Protocols Allow Quick, Efficient Communication At The Risk Of Data Errors And Packet Loss. Connectionless Protocols Are A Good Choice Where:
Speed Is Important
Smaller Chunks Of Data Are Being Sent
◙ - ➤ For More About - > OSI REFERENCES 7 LAYERS:
LAN SWITCHING
◙ - ➤ For More About - > COLLECTION OF NETWORKING CONCEPTS:
◙ - ➤ For More About - > ROUTER, SWITCH (Layer 2 And Layer 3), BRIDGE AND HUB:
Switches Can Connect Different Networks Types (Such As Ethernet And Fast Ethernet) Or Networks Of The Same Type. Many Switches Today Offer High-Speed Links, Like Fast Ethernet Or FDDI, That Can Be Used To Link The Switches Together Or To Give Added Bandwidth To Important Servers That Get A Lot Of Traffic. A Network Composed Of A Number Of Switches Linked Together Via These Fast Uplinks Is Called A "Collapsed Backbone" Network.Dedicating Ports On Switches To Individual Nodes Is Another Way To Speed Access For Critical Computers. Servers And Power Users Can Take Advantage Of A Full Segment For One Node, So Some Networks Connect High Traffic Nodes To A Dedicated Switch Port.
Switches Normally Have Higher Port Counts Than Bridges And Divide Network Into Several Dedicated Channels Parallel To Each Other. These Multiple Independent Data Paths Increase The Throughput Capacity Of A Switch. There Is No Contention To Gain Access And LAN Switch Architecture Is Scalable. Another Advantage Of Switches Is That Most Of Them Are Self Configuring, Minimizing Network Downtime, Although Ways For Manual Configuration Are Also Available.
If A Segment Is Attached To A Port Of A Switch Then CSMA/CD Is Used For Media Access In That Segment. However, If The Port Has Only One Station Attached Then There Is No Need For Any Media Access Protocol. The Basic Operation Of A Switch Is Like A Multiport Bridge. The Source And Destination Medium Access Control (MAC) Address Of Incoming Frame Is Looked Up And If The Frame Is To Be Forwarded, It Is Sent To The Destination Port. Although This Is Mostly What All Switches Do, There Are A Variety Of Features That Distinguish Them, Like The Following.
HOW CAN LAN SWITCHING HELP: Full Duplex Mode Of Ethernet Allows Simultaneous Flow Of Traffic From One Station To Another Without Collision. So, Ethernet In Full Duplex Mode Doesn't Require Collision Detection When Only One Port Station Is Attached To Each Port. There Is No Contention Between Stations To Transmit Over A Medium, And A Station Can Transmit Whenever A Frame Is Queued In The Adapter. The Station Can Also Receive At The Same Time. This Has A Potential To Double The Performance Of The Server.
An Ethernet, Token Ring And FDDI All Use Shared Media. Conventional Ethernet Is Bridged Or Routed. A 100 Mbps Ethernet Will Have To Divide Its Bandwidth Over A Number Of Users Because Of Shared Access. However With A Switched Network One Can Connect Each Port Directly So Bandwidth Is Shared Only Among A Number Of Users In A Workgroup (Connected To The Ports). Full Duplex Is Another Method To Increase Bandwidth To Dedicated Workstations Or Servers. To Use Full Duplex, Both Network Interface Cards Used In The Server Or Workstation, And The Switch Must Support Full Duplex Operation. Full Duplex Doubles The Potential Bandwidth On That Link, Providing 20 Mbps For Ethernet And 200 Mbps For Fast Ethernet.
◙ - ➤ For More About - > ETHERNET SWITCHING:
SWITCHES: A Switch Is A Layer 2 (Data Link) Device With Physical Ports And That The Switch Communicates Via Frames That Are Placed On To The Wire At Layer 1 (Physical). Switches Are Generally Identified As LAYER-2 Devices, As Switches Process Information Stored In The DATA-LINK Header Of A Frame (Such As Mac Addresses In Ethernet). The Switch Will Build The MAC-Address Table By Examining The Source MAC Address Of Each Frame.◙ One Collision Domain Per Port.
◙ One Broadcast Domain Across All Switches
◙ - ➤ For More About - > BROADCAST DOMAINS Vs COLLISION DOMAINS:
◙ - ➤ Switches Create A Virtual Circuit Between Two Connected Devices, Establishing A Dedicated Communication Path Between Two Devices.◙ - ➤ Switches On The Network Provide Microsegmentation.
◙ - ➤ This Allows Maximum Utilization Of The Available Bandwidth.
◙ - ➤ A Switch Is Also Able To Facilitate Multiple, Simultaneous Virtual Circuit Connections.
◙ - ➤ Broadcast Frames To All Connected Devices On The Network.
◙ - ➤ Switches Are Also Known As Learning Bridges Or Learning Switches.
◙ - ➤ A Switch Has A Source Address Table In Cache (RAM) Where It Stores Source MAC Address After It Learns About Them.
◙ - ➤ A Switch Receives An Ethernet Frame It Searches The Source Address Table For The Destination MAC Address.
◙ - ➤ If It Finds A Match, It Filters The Frame By Only Sending It Out That Port.
◙ - ➤ If There Is Not A Match If Floods It Out All Ports.
◙ - ➤ If A Switch Has The Frame’s Destination Address In Its CAM Table (Or Source Address Table) It Will Only Send The Frame Out The Appropriate Port.
◙ - ➤ If A Switch Does Not Have The Frame’s Destination MAC Address In Its CAM Table, It Floods (Sends) It Out All Ports Except For The Incoming Port (The Port That The Frame Came In On) Known As An Unknown Unicast, Or If The Destination MAC Address Is A Broadcast.
ADVANTAGES OF ETHERNET SWITCHES: ◙ - ➤ Significant Bandwidth Improvement By Limiting A Collision Domain To A Single Port.
◙ - ➤ Scalability. Repeater Rules Are Limited To A Single Port.
◙ - ➤ VLAN Capability. Broadcast Domains Can Be Located Logically And Are Not Limited By Geographical Boundaries.
◙ - ➤ Enhanced Security.
◙ - ➤ Full-Duplex Capability.
SWITCHING METHODS: LAN Switching Is Used To Forward Or Filter Frames Based On Their Hardware Destination. However, There Are Three Different Methods In Which Frames Can Be Forwarded Or Filtered. Each Method Has Its Advantages And Disadvantages, And By Understanding The Different LAN Switch Methods Available, You Can Make Smart Switching Decisions.
◙ - ➤ STORE-AND-FORWARD: With The Store-And-Forward Mode, The Complete Data Frame Is Received On The Switch's Buffer, A Cyclic Redundancy Check (CRC) Is Run, And Then The Destination Address Is Looked Up In The MAC Filter Table.
– The Entire Frame Is Received Before Any Forwarding Takes Place.
– The Destination And Source Addresses Are Read And Filters Are Applied Before The Frame Is Forwarded.
– CRC Check Done
◙ - ➤ CUT-THROUGH: With The Cut-Through Mode, The Switch Waits For Only The Destination Hardware Address To Be Received And Then Looks Up The Destination Address In The MAC Filter Table.
– The Frame Is Forwarded Through The Switch Before The Entire Frame Is Received.
– This Mode Decreases The Latency Of The Transmission, But Also Reduces Error Detection.
◙ - ➤ CUT-THROUGH (FAST-FORWARD): – Offers The Lowest Level Of Latency.
– Fast-Forward Switching Immediately Forwards A Packet After Reading The Destination Address.
– There May Be Times When Packets Are Relayed With Errors.
– Although This Occurs Infrequently And The Destination Network Adapter Will Discard The Faulty Packet Upon Receipt.
◙ - ➤ CUT-THROUGH (FRAGMENT-FREE): Fragment-free Is The Default Mode For The Catalyst 1900 Switch; It Is Sometimes Referred To As Modified Cut-Through Checks The First 64 Bytes Of A Frame For Fragmentation (Because Of Possible Collisions) Before Forwarding The Frame.
– Fragment-Free Switching Filters Out Collision Fragments Before Forwarding Begins.
– Collision Fragments Are The Majority Of Packet Errors.
– In A Properly Functioning Network, Collision Fragments Must Be Smaller Than 64 Bytes.
– Anything Greater Than 64 Bytes Is A Valid Packet And Is Usually Received Without Error.
– Fragment-Free Switching Waits Until The Packet Is Determined Not To Be A Collision Fragment Before Forwarding.
ROUTERS: A Router Is A Layer 3 (Network) Devices That Communicates With Other Routers With The Use Of Packets, Which In Turn Are Encapsulated Inside Frames. Routers Have Interfaces For Connection Into The Network Medium.
◙ - ➤ A Router Is A Layer 3 Device.
◙ - ➤ Used To “Route” Traffic Between Two Or More Layer 3 Networks.
◙ - ➤ Routers Make Decisions Based On Groups Of Network Addresses, Or Classes, As Opposed To Individual Layer 2 MAC Addresses.
◙ - ➤ Routers Use Routing Tables To Record The Layer 3 Addresses Of The Networks That Are Directly Connected To The Local Interfaces And Network Paths Learned From Neighboring Routers.
◙ - ➤ Routers Are Not Compelled To Forward Broadcasts.
Mac Addresses And IP Addresses And The Different Layers, Routing Operates At Layer 3, Where Packets Are Sent To A Specific Next-Hop IP Address, Based On Destination IP Address. It Is Important To Remember That Switches Are OSI Layer 2 Devices And Mac Addresses Are Layer 2 Addresses. Switches Do Not Read IP Addresses. IP Addresses Are Layer 3 Addresses. Switches Don't Get Information About The Mac Addresses In Other Networks Because They Can Not Read Any Protocol That Can Go Over A Router. They Are Just Layer 2.
If TWO PC's Are Connected To The Same Switch, They Belong To The Same Subnet, And Not Different Subnets. Two PCs On Different Subnets (VLANs) Would Not Be Able To Ping Each Other Unless There Is A Layer 3 Device (I.E. A Router).
VLANs Divide Broadcast Domains In A LAN Environment, Switches Operate At Layer2 (Data link Layer). VLANS Cannot Communicate Without L3 (Network Layer), Whenever Hosts In One VLAN Need To Communicate With Hosts In Another VLAN, The Traffic Must Be Routed Between Them. This Is Known As Inter-VLAN Routing. Layer 2 Switching Use For Workgroup Connectivity And Network Segmentation (Breaking Up Collision Domains). This Allows You To Create A Flatter Network Design And One With More Network Segments Than Traditional 10baset Shared Networks. Layer 2 Switching Has Helped Develop New Components In The Network Infrastructure.
DIFFERENCES BETWEEN LAYER 2, LAYER 3 AND LAYER 4 SWITCHING
LAYER 2 SWITCHING (Layer 2 Switch As A Multiport Bridge) - Layer 2 Switching Provides The Following: ✓ Hardware-Based Bridging (Mac)
✓ Wire Speed
✓ High Speed
✓ Low Latency
✓ Low Cost
LAYER 2 SWITCHING Is Hardware Based, Which Means It Uses The Media Access Control (MAC) Address From The Host’s Network Interface Cards (NICs) To Filter The Network. Switches Use Application-Specific Integrated Circuits.
LAYER 2 SWITCH Traditional Switching Operates At Layer 2 Of The OSI Model, Where Packets Are Sent To A Specific Switch Port Based On Destination MAC Addresses And Devices In The Same Layer 2 Segment Do Not Need Routing To Reach Local Peers.
On LAYER 2 SWITCHING Protocols And Concepts Used To Improve Redundancy, Propagate VLAN Information, And Secure The Portion Of The Network Where Most Users Access Network Services. Switches Only Know The Mac Addresses Of The Hosts That Are Either Connected Directly To Their Ports And Have Already Sent At Least 1 Frame Or The Mac Addresses Of Other Switches That They Are Able To Talk To.
Layer 2 Forwarding Table -The Destination MAC Is Checked Against The CAM Table To Determine If The Frame Contains A Layer 3 Packet (If The MAC Address Belongs To A Layer 3 interface on the switch).
LAYER 2 SWITCHING Is So Efficient Because There Is No Modification To The Data Packet, Only To The Frame Encapsulation Of The Packet, And Only When The Data Packet Is Passing Through Dissimilar Media (Such As From Ethernet To FDDI).
Remember That Layer 2 Switches Break Up Collision Domains, But The Network Is Still One Large Broadcast Domain. Layer 2 Switches Break Up Collision Domains On Each Port, But All Ports Are Still Considered, By Default, To Be In One Large Broadcast Domain.
◙ - ➤ For More About - > BROADCAST DOMAINS Vs COLLISION DOMAINS:
Mac Addresses And IP Addresses And The Different Layers, Routing Operates At Layer 3, Where Packets Are Sent To A Specific Next-Hop IP Address, Based On Destination IP Address. It Is Important To Remember That Switches Are OSI Layer 2 Devices And Mac Addresses Are Layer 2 Addresses. Switches Do Not Read IP Addresses. IP Addresses Are Layer 3 Addresses. Switches Don't Get Information About The Mac Addresses In Other Networks Because They Can Not Read Any Protocol That Can Go Over A Router. They Are Just Layer 2. If 2 Pc's Are Connected To The Same Switch, They Belong To The Same Subnet, And Not Different Subnets. Two PCs On Different Subnets (VLANs) Would Not Be Able To Ping Each Other Unless There Is A Layer 3 Device (I.E. A Router). Recall From The ISO OSI Reference Model That Layer 3 Devices Allow For Interconnectivity Between Networks.Routers Are Used To Connect And Segment (Separate) Networks (Subnets) This Also Means That They Split Up Broadcast Domains. Switches Do Break Up Collision Domains As Do Routers.
LIMITATIONS OF LAYER 2 SWITCHING: Layer 2 Switches Have The Same Limitations As Bridge Networks. Remember That Bridges Are Good If You Design The Network By The 80/20 Rule. The Old 80/20 Rule Is That 80% Of The Traffic Was On Their Local Segment And Only 20% Of The Network Traffic Went Over The Backbone (End-To-End VLANs ---> Follow The 80/20 Rule = 80% Local 20 % Across Core).
Bridged Networks Break Up Collision Domains, But The Network Is Still One Large Broadcast Domain. Similarly, Layer 2 Switches (Bridges) Cannot Break Up Broadcast Domains, Which Can Cause Performance Issues And Limits The Size Of Your Network. Broadcast And Multicasts, Along With The Slow Convergence Of Spanning Tree, Can Cause Major Problems As The Network Grows. Because Of These Problems, Layer 2 Switches Cannot Completely Replace Routers In The Internetwork.
ALSO KNOW END-TO-END VLAN: Those VLAN Who Travels All The Way From One Access Switch To Another Access Switch Directly, Without The Help Of Router. VLANs Are Locally To The Switch, Every Switch Will Have Unique VLANs Configured (To Prevent The L-2 Broadcast In Your Access Network). So Whenever You Want To Access Other VLANs Or The Users Sitting In Different Access Switches You Need To Go To The Router, Which Is Very Likely In This Design. So Considering This Only 20% Of The Traffic Resides In Your Switch And 80% Of The Traffic Travels From Access--> Core / Distribution
ALSO KNOW NETWORK-DESIGN 80/20 Vs 20/80 Rule: 80/20 Vs 20/80 Rule Is Related To The Traffic Pattern. Does One User/Resource In That Particular VLAN Communicates Mostly Inside The VLAN Or Outside. In The Early Days Of Networking Traffic Was Mostly 80/20, Which Dictates That 80 Percent Of The Traffic Remains On The Local Network, And Only 20 Percent Should Be Routed To Another Network.
But For Quite A Few Years Now It Has Shifted To 20/80. Because Routing Introduces More Latency Than Switching, The 20/80 Rule Has Dictated A Need For A Faster Layer 3 Technology, Namely Layer 3 Switching.
CISCO DEVELOPED A HIERARCHICAL MODEL TO SERVE AS A GUIDELINE TO PROPER NETWORK DESIGN. THIS MODEL IS SEPARATED INTO THREE LAYERS: ACCESS LAYER – The Access Layer Is Where The End User Connects Into The Network. Access Layer Switches Generally Have A High Number Of Low-Cost Ports Per Switch, And VLANs Are Usually Configured At This Layer. In A Distributed Environment (80/20 Rule), Servers And Other Such Resources Are Kept Close To Users In The Access Layer.
DISTRIBUTION LAYER – The Distribution Layer Provides End Users With Access To The Core (Backbone) Layer. Security (Using Access-Lists) And QOS Are Usually Configured At The Distribution Layer.
CORE LAYER – The Core Layer Is The “Backbone” Of The Network. The Core Layer Is Concerned With Switching Data Quickly And Efficiently Between All Other “Layers” Or “Sections” Of The Network. In A Centralized Environment (20/80 Rule)
Servers And Other Such Resources Are Placed In Their Own “Dedicated” Access Layer, And The Core Layer Must Switch Traffic From All Other Access Layers To This Server Block.
LAYER 3 SWITCHES
A LAYER 3 SWITCH Is A High-Performance Device (Switching Is A Hybrid) For Network Routing. Layer 3 Switches Actually Differ Very Little From Routers. The Only Difference Between A Layer 3 Switch And A Router Is The Way The Administrator Creates The Physical Implementation. Also, Traditional Routers Use Microprocessors To Make Forwarding Decisions, And The Switch Performs Only Hardware-Based Packet Switching.
However, Some Traditional Routers Can Have Other Hardware Functions As Well In Some Of The Higher-End Models. Layer 3 Switches Can Be Placed Anywhere In The Network Because They Handle High-Performance LAN Traffic And Can Cost-Effectively Replace Routers. A Layer 3 Switch Can Support The Same Routing Protocols As Network Routers Do.
There Are Different Types Of Layer 3 Switching, Route Caching And Topology-Based. In Route Caching The Switch Required Both A Route Processor (RP) And A Switch Engine (SE). The RP Must Listen To The First Packet To Determine The Destination. At That Point The Switch Engine Makes A Shortcut Entry In The Caching Table For The Rest Of The Packets To Follow. Due To Advancement In Processing Power And Drastic Reductions In The Cost Of Memory, Today’s Higher End Layer 3 Switches Implement A Topology-Based Switching Which Builds A Look Up Table And Populates It With The Entire Network’s Topology. The Database Is Held In Hardware And Is Referenced There To Maintain High Throughput. It Utilizes The Longest Address Match As The Layer 3 Destination.
Inter-VLAN Routing And Also Ensuring The Performance Of The LAN Is Not Degraded Has Been To Implement Layer 3 Switches, Which Are Essentially Layer 2 Switches With A Routing Engine That Is Designed To Specifically Route Traffic Between VLANs In A LAN Environment.
USING LAYER 3 SWITCHES FOR INTER-VLAN ROUTING AS OPPOSED TO TRADITIONAL ROUTERS IS POPULAR AND RECOMMENDED FOR THE FOLLOWING REASONS: It Is Important To Understand The Difference Between Layer 3 Routing And Layer 3 Switching. Both Terms Are Open To Some Interpretation; However, The Distinction Between Both Can Perhaps Be Best Explained By Examining How An IP Packet Is Routed. The Process Of Routing An IP Packet Can Be Divided Into Two Distinct Processes:
CONTROL PLANE: The Control Plane Process Is Responsible For Building And Maintaining The IP Routing Table, Which Defines Where An IP Packet Should Be Routed To Based Upon The Destination Address Of The Packet, Which Is Defined In Terms Of A Next Hop IP Address And The Egress Interface That The Next Hop Is Reachable From. Layer 3 Routing Generally Refers To Control Plane Operations.
The Control Plane Is The Component To A Router That Focuses On How That One Individual Box Interacts With Its Neighbors With State Exchange. The Routing Information (Data) Base (RIB) And Label Information Base (LIB) Are Processed In Software And Used To Populate FIB (Forwarding Information Base) And The LFIB.
The Control Plane Is Where Forwarding/Routing Decisions Are Made. Switches And Routers Have To Figure Where To Send Frames (L2) And Packets (L3). The Switches And Routers That Run The Network Run As Discrete Components, But Since They Are In A Network, They Have To Exchange Information Such As Host Reachability, Status, Etc, With Neighbors. This Is Done In The Control Plane Using Protocols Like Spanning Tree, OSPF, BGP, QOS Enforcement, Etc.
DATA PLANE: The Data Plane Process Is Responsible For Actually Routing An IP Packet, Based Upon Information Learned By The Control Plane. Whereas The Control Plane Defines Where An IP Packet Should Be Routed To, The Data Plane Defines Exactly How An IP Packet Should Be Routed.
This Information Includes The Underlying Layer 2 Addressing Required For The IP Packet So That It Reaches The Next Hop Destination, As Well As Other Operations Required On For IP Routing, Such As Decrementing The Time-To-Live (TTL) Field And Recomputing The IP Header Checksum. Layer 3 Switching Generally Refers To Data Plane Operations.
The Data Plane Is Where The Action Takes Place. It Includes Things Like The Forwarding Tables, Routing Tables, ARP Tables, Queue's, Tagging And Re-Tagging, Etc. The Data Plane Carries Out The Commands Of The Control Plane.
The Data Plane Is The Workhorse Of The Switching Elements In Our Networks. It Has The Responsibility Of Parsing Packet Headers (Or Cells, SONET) In High Speed Search Asics. It Manages QOS, Filtering, Encapsulations, Queuing, Policing All Of The Reasons We Had And Still Do In Many Cases Purpose Built Silicon Or Custom ASIC Designs.
The Data/Forwarding Plane Must Do Those Operations In The “Fast Path” To Keep Up With Performance Needs In Data Centers And Core Networks. Achieving That Sort Of Performance Is Often Done With Varying Components Of Memory Types Whether Trie Based BCAM, TCAM, NPU And Even FPGA Is Starting To Post Impressive Numbers.
The Fundamental Difference Between A Layer 3 Switch And A Router Is That Layer 3 Switches Have Optimized Hardware Passing Data Traffic As Fast As Layer 2 Switches. However, Layer 3 Switches Make Decisions Regarding How To Transmit Traffic At Layer 3, Just As A Router Does.
LAYER 4 SWITCHES
LAYER 4 SWITCHING Provides Additional Routing Above Layer 3 By Using The Port Numbers Found In The Transport Layer Header To Make Routing Decisions. These Port Numbers Are Found In Request For Comments (RFC) 1700 And Reference The Upper-Layer Protocol, Program, Or Application. Layer 4 Information Has Been Used To Help Make Routing Decisions For Quite A While.
LAYER 4 SWITCHES Are Capable Of Identifying Which Application Protocols (HTTP, SNTP, FTP, And So Forth) Are Included With Each Packet, And Use This Information To Hand Off The Packet To The Appropriate Higher-Layer Software.
Because Layer 4 Devices Enable You To Establish Priorities For Network Traffic Based On Application, You Can Assign A High Priority To Packets Belonging To Your Vital In-House Applications, With Different Forwarding Rules For Low-Priority Packets.
LAYER 4 SWITCHES Also Provide An Effective Wire-Speed Security Shield For A Network Because Any Company- Or Industry-Specific Protocols Can Be Confined To Only Authorized Switched Ports Or Users. This Security Feature Is Often Reinforced With Traffic Filtering And Forwarding Features.
A LAYER 4 SWITCH Also Must Allocate A Large Amount Of Memory To Its Forwarding Tables. Layer 2 And Layer 3 Devices Have Forwarding Tables Based On MAC And Network Addresses, Making Those Tables Only As Large As The Number Of Network Devices. Layer 4 Devices, However, Must Keep Track Of Application Protocols And Conversations Occurring In The Network. Their Forwarding Tables Become Proportional To The Number Of Network Devices Multiplied By The Number Of Applications.
The Largest Benefit Of Layer 4 Switching Is That The Network Administrator Can Configure A Layer 4 Switch To Prioritize Data Traffic By Application, Which Means A Qos Can Be Defined For Each User. For Example, A Number Of Users Can Be Defined As A Video Group And Be Assigned More Priority, Or Band- Width, Based On The Need For Videoconferencing.
MULTI-LAYER SWITCHING (MLS)
Multilayer Switches Are Important For Networks Using ATM And Gigabit Ethernet. Although The Definition For Multilayer Switches Is Not Standardized, They Can Be Described As Switches That Besides MAC Layer Routing, Have Some Routing Layer Functionality Like Multicast And Broadcast Containment, Some VLAN Services, And Packet Filtering And Firewalling Between Two Vlans. They May Also Support Transmission Control Protocol/Internet Protocol (TCP/IP) And Internetwork Packet Exchange (IPX) Routing. Many Of Thse Switches Provide Support For Frame And Cell Switching.
One Of The Most Important Features Would Be That It Provides Gigabit Level Scaling. This Makes It Easier And Cheaper To Upgrade The Network In Future When The Demands On Network Increases. Using Policy Based VLAN, Support For Various Classes Of Service And Quality Of Service Can Be Provided. Thus Offering Features That Were Once Available Only In ATM Networks.
Cisco Switches Perform Multilayer Switching At Layer 3 And Layer 4. At Layer 3, The Catalyst Family Of Switches Caches Traffic Flows Based On IP Addresses. At Layer 4, Traffic Flows Are Cached Based On Source And Destination Addresses, In Addition To Source And Destination Ports. All Switching Is Performed In Hardware, Providing Equal Performance At Both Layer 3 And Layer 4 Switching.
MULTI SWITCH ROUTERS (MSRs)
ROUTE SWITCH MODULES (RSMs)
From The Perspective Of The Catalyst Switch, The RSM Appears As A Module With A Single Trunked Port And One Media Access Control (MAC) Address. From The Perspective Of The User, The RSM Has One Port. This Port Is Unlike Other Catalyst Switch Line Card Ports In That It Has No External Attributes Such As Media Type Or Speed.
An RSM Is Essentially A Cisco Router On An Add-In Module That Plugs Directly Into The Backplane Of A Catalyst 5000 Switch. The Main Benefit Of Using An RSM Is That It Eliminates The Need For An External Router, Thus Speeding Up The Routing Process.
However, An RSM Is Still A Router In The Traditional Sense. Although The Fact That Packets Do Not Need To Be Passed To An External Device Makes The Process A Little Faster, Routing Is Still Occurring Using The IOS Software, Using Traditional Routing Methods. As Such, A Catalyst 5000 With An RSM Installed Can Still Be Considered A Layer 3 Switch, But Will Not Provide The Dramatic Increases In Speed That Other Methods Listed Here Do. More Than Anything, The RSM Provides Convenience, Adding Routing Capabilities To A Layer 2 Switch.
You Need To Add An RSM To A Layer 2 Device For Example, A 5000 Catalyst Switch--To Be Able To Provide Switching Of Layer 3 Packets Without A Router. An RSM Makes Layer 2 Switches A Multi-Layer Switch And Can Integrate Layer 2 And Layer 3 Functionality In A Single Box. The 5000 Series Uses The RSM Or A Route Switch Feature Card (RSFC), And The 6000 Series Uses The Multilayer Switch Module (MSM) To Perform This Function. The RSM, RSFC, And MSM Are Configured In Exactly The Same Way On The Switch. The RSM Is A Module Plugged Directly Into The Switch, Which Runs The Cisco IOS In Order To Perform Inter-VLAN Communication. The 5000 Series Switch Sees The RSM As A Single Trunked Port And A Single MAC Address. In Other Words, It Appears As A Router On A Stick To The Switch.
The RSM Inter- Face To The Switch Is Through VLAN 0 And VLAN 1. VLAN 0 Is Not Accessible To The Administrator. The RSM Uses Two Channels, And VLAN 0 Maps To Channel 0, Which Supports Communication Between The RSM And The Catalyst 5000 Series Default VLAN (VLAN 1). VLAN 1 Maps To Channel 1. The MAC Address Assigned To The RSM Is From The Programmable Read Only Memory (PROM) On The Line Communication Processor (LCP). This MAC Address Is Used To Identify The Slot Of The RSM And For Diagnostics.
The MAC Addresses For VLAN 1 Are Assigned From A PROM That Contains 512 MAC Addresses. All Routing Interfaces Except VLAN 0 Use The Base MAC Address. The RSFC Is A Daughter Card For The Supervisor Engine II G And Supervisor III G Cards. The RSFC Is A Fully Functioning Router Running The Cisco IOS.
The MSM Uses Four Full-Duplex Gigabit Ethernet Interfaces To Connect To The Switch And Looks Like An External Router To The Switch. These Four Inter- Faces Can Be Four Separate Links For Four Different Vlans, Or They Can Be Trunked And Configured As One Load-Balanced Link Running Etherchannel And ISL Or 802.1q. Subinterfaces Are Then Used To Configure Each VLAN.
CONCLUSION:
The Goal Of This Article Is To Give An Easy Way To Understand The “LAYER 2, LAYER 3AND LAYER 4 SWITCH COMPARISON " And Also We Hope This Guide Will Help Every Beginner Who Are Going To Start Cisco Lab Practice Without Any Doubts. Some Topics That You Might Want To Pursue On Your Own That We Did Not Cover In This Article Are Listed Here! Hands - On Experience Is An Invaluable Part Of Preparing For The Lab Exam And Never Pass Up An Opportunity To Configure Or Troubleshoot A Router ( If You Have Access To Lab Facilities, Take Full Advantage Of Them) There Is No Replacement For The Experience You Can Gain From Working In A Lab, Where You Can Configure Whatever You Want To Configure And Introduce Whatever Problems You Want To Introduce, Without Risk Of Disrupting A Production Network. Thank You And Best Of LuckThis Article Written Author By: Mr. Premakumar Thevathasan - CCNA And CCNP (Routing & Switching), MCSE, MCSA, MCSA - MSG, CIW Security Analyst, CompTIA Certified A+ And Etc.
WARNING AND DISCLAIMER:
Routers Direct And Control Much Of The Data Flowing Across Computer Networks. This Guide Provides Technical Guidance Intended To Help All Network Students, Network Administrators And Security Officers Improve Of Their Demonstrated Ability To Achieve Specific objectives Within Set Timeframes. We Cannot Provide Any Kind Of Advice, Explanation, Opinion, Or Recommendation And This Document Carries No Explicit Or Implied Warranty. Nor Is There Any Guarantee That The Information Contained In This Document Is Accurate. Every Effort Has Been Made To Make All Articles As Complete And As Accurate As Possible, But No Warranty Or Fitness Is Implied. Your Access To The Website Is At Your Own Risk, It Is Offered In The Hopes Of Helping Others, But You Use It At Your Own Risk Only. The Author Will Not Be Liable For Any Special, Incidental, Consequential Or Indirect Any Damages Due To Loss Of Data Or Any Other Reason That Occur As A Result Of Using This Document. But No Warranty Or Fitness Is Implied. The Information Provided Is On An "As Is" Basic. All Use Is Completely At Your Own Risk. Your Access To The Website Is Subject To Our Terms Of Use.Home Page Of - > The School Of Cisco Networking (SCN) Page Of - > SCN InF4 TECH (IT Consultancy & Services) About Us SCN Page To Send Email @
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